Limit switch apparatus



Sept. 28, 1965 E. A. TOWNSEN 3,208,729

LIMIT SWITCH APPARATUS Filed Dec. 11, 1961 2 Sheets-Sheet 1 Agent Sept.28, 1965 A. TOWNSEN 3,208,729

LIMIT SWITCH APPARATUS Filed Dec. 11, 1961 2 Sheets-Sheet 2 FlG.5

IN VEN TOR.

EUGENE ALEXANDER TOWNSEN 2 Agent United States Patent 3,208,729 LIMITSWITCH APPARATUS Eugene Alexander Townsen, Burbank, 'Calif., assignor toLockheed Aircraft Corporation, Los Angeles, Calif. Filed Dec. 11, 1961,Ser. No. 158,270 3 Claims. (Cl. 254173) The present invention relates tolimit switches and, more particularly, to a limit switch apparatus forpreventing the overlap of a cable on a crane and hoist apparatus.

As is well-known, crane and hoist apparatus usually utilize a drum uponwhich a cable is spirally wound and unwound, such drum being powered byan engine or electric motor; The peripheral surface of the drum may heprovided with circumferentially spiraled grooves into which the cablewill fall when the cable is wound upon the drum so that the cable willbe spirally wound without crossing or climbing or otherwise overlappingupon itself. Severe problems occur if the cable accidentally over-lapsduring the lifting operation. For example, such overlapping may causethe cable to break thus dropping the load or, during continued windingor subsequent unwinding, the overlapped portion of the cable maysuddenly sli into its proper position on the drum, such slip causing asevere shock to the load which may either damage the load or cause thecable to break. Obviously, the breaking of a cable presents a serioushazard to both the load itself and any personnel who may be working inthe area adjacent therebelow.

Therefore, it is one of the objects of the present invention to providea limit switch for automatically stopping the drive means on a cable,crane and hoist apparatus when the cable is in an overlapping condition.

Another object of the present invention is to provide limit switchapparatus for automatically sensing a cable overlap condition forcausing stopping of the cable drive means;

A further object of the present invention is the provision of apparatus.and method for automatically sensing a radial projection anywhere alongthe peripheral length of a relatively long cylindrical device.

According to the present invention, limit switch apparatus is providedfor axially fixed disposition adjacent the peripheral surface of a cabledrum along the length thereof and comprises a sensing bar memberparallel to the drum axis and located a distance less than the diameterof the cable from the peripheral surface of the drum, such peripherybeing defined for the purposes hereof as the normal maximum radiallyouter location of the cable, a pair of rod members each having one endelfectively connect-ed to respective opposite ends of such sensing barmember and extending therefrom in a direction radial to the drum, andswitch means coupled to the other ends of such rod members for actuationthereby, such switch means being connected into the control device forthe drive means of the cable drum. In operation, overlapping of thecable upon itself at any point along the peripheral length of the cabledrum will cause the overlapping portion of the cable to contact thesensing bar member and move either or both of the bar member ends in aradially outward direction, thus causing one or more of the rod membersto be moved for I ctuating the switch means. If the overlapped conditionoccurs near the middle of the length of the sensing bar member, the rodmembers may be displaced substantially 3,208,729 Patented Sept. 28, 1965equal amounts; if the overlapping occurs closer to one of the sensingbar member ends than the other, the corresponding rod member will bedisplaced a relatively greater amount but in any event, .at least one ofthe rod members will be displaced a distance at least equal to theabnormal projection distance of the cable, and such displacement ofeither or both of the rod members will cause actuation of the switchmeans.

In a preferred embodiment of the present invention, the switch meanscomprises a pair of switches of the microswitch type which aremechanically separate from each other but in electrical series, eachswitch having .a finger member pivoted at one end thereof and coupled tothe corresponding rod member at the other end thereof, with a switchcontact 'button located in abutment with the middle of such fingermember for actuation by movement thereof.

The features of the present invention which are [believed to be novelare set forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages thereof, may best be understood byreference to the following description, taken in connection with theaccompanying drawings, in which:

FIGURE 1 is a perspective view of the cable drum portion of a crane andhoist apparatus showing a preferred embodiment of the present inventionmounted thereon;

FIGURE 2 is an enlarged iiragmentary elevation View, partly in section,of the apparatus illustrated in FIGURE 1; and

FIGURE 3 is a further enlarged fragmentary elevation view showing theposition of the apparatus when the cable is in an overlap position.

Referring to the drawings, a cable drum 10 is provided with a drumshield 111 having a cutaway bottom opening 12 to permit the cable 16 tomove freely around the drum 10. In the embodiment illustrated, the drum10 is provided with a spiral groove l1-4 for guiding the cable '13 inspiral progression from the left end '15 to the right end 16 of thecable-bearing portion of the drum 10. The groove I14 is divided alongits spiral length by a ridge 17 of finite thickness to permit separationof each coil of the cable '13 along the drum surface. A pair of switches'18 and 19 are mounted on the exterior surface '20 of the drum shield 11 [by means of respective mounting blocks 21 and :22 which, in turn, aresecured to the drum shield l1i1 by respective brackets 23 and Q4 whichare welded or otherwise secured to the drum shield 11. Mounting blocks21 and .2-2 have respective bores Q5 and 26 which are radial to the axisof the drum 10 and receive respective rod members 27 and 28there-through in freely slidabl-e relationship with sufficient clearanceto permit a slight amount of lateral movement of the rods 27 and 2-8, aswill be explained more fully herein-after. The drum shield 11 similarlyis provided with bore holes 29 and 30. The rod members .27 and .28 areprovided with respective threaded ends 31 and 6'2 by which they arethreadvably secured to pivotal blocks 33 and 34, respectively. Blocks 33and 34 are disposed within respective apertures 35 and '36 near theopposite ends 37 and 38 of a sensing bar member 3-9 which has a lengthat least equal to the cable-bearing axial length of the cable drum 10.The blocks 33 and 34 are mounted to the sensing bar member 39 byrespective pivot pins 40 and 41 so as to rotate about axes tangential tothe drum 10. The threaded ends 31 and 32 of the rod members 27 and :28are secured to the blocks I33 and 34 in a position eccentric to thepivot pins 40 and 441 so that tilt-ing of the sensing bar member 39 atan angle to the drum axis will cause the blocks 33 and '34 to rotate ontheir respective pivot pins 40 and 41 to prevent undue lateral stress onthe rod members 27 and 28. The rod members 27 and 28 are each providedwith a plurality of stop means comprising lock nuts which will bedescribed only in connection with rod member 28, as particularly seen inFIGURE 3, because of the symmetry of the apparatus.

Referring to FIGURE 3, the rod member 28 may be threaded over its entirelength or, at least, from both of its ends a suflicient distance for theappropriate disposition of the various lock nuts which will be hereindesignated in pairs. Lock nuts 42 are secured to the rod member 28 so asto normally rest upon the mounting block 22 and provide an adjustmentfor the distance between the sensing bar member 39 and the cable drum10. A spring 44 serves to provide shock absorption as well as to urgethe sensing bar member 39 downwardly in opposition to the action of aspring 46 which is compressed between lock nuts 47 and a finger member48 of the switch 19. Lock nuts 47 are tightened against spring 46 untilthe finger member 48 has depressed the push button 49 of the switch 19to cause contact between the inner contacts (not shown) of the switch19, the construction and the operation of the latter being well-known inthe art. Then the lock nuts 50 are secured to the rod member 28 in aposition of abutment against the finger member 48 so that, upon upwardmovement of the rod member 28 in response to sensing action of thesensing bar member 39, the lock nuts 50 will push the finger member 48upwardly about its pivot pin 51 to release the push button 49 foropening the contacts of the switch 19.

The proximal edge or surface 52 of the sensing bar member 39 is adjustedby means of the lock nuts 42 on both of the rod members 27 and 28 so asto be parallel to the plane of the radially outer extremities 53 of thecable 13, which plane constitutes the effective peripheral surface ofthe cable-drum apparatus, and spaced a distance therefrom less than anyabnormal projection of the cable 13 y from thecable-drum 10, suchprojection being caused by series-connected switches 18 and 19 isconnected into the electricalcontrol system for the cable windingoperation in any convenient and well-known manner so that, uponactuation of the cable overlap sensing mechanism to open either or bothof the switches, the cable winding operation will immediately cease.Thus, as the cable 13 is wound upon the drum 10, the occurrence of anabnormal projection of a portion of the cable 13, such as is shown inFIGURE 3, will cause either or both of the ends of the sensing barmember 39 to be forcibly moved by such cable portion in a radiallyoutward direction from the cable-drum to move either or both of the rodmembers 27 and 28 upwardly whereby the lock nuts 50 will release theengagement of the finger member 48 from the push button 49 to open thecontacts of the corresponding switch. Since the sensing bar member 39 isof a length at least equal to the cable-bearing length of the drum 10,

the sensing bar member 39 will be responsive to such abnormal projectionof the cable 13 anywhere along such length. The maximum deflection ofthe push button 49 by the finger member 48 is chosen to be less than theminimum possible displacement of either of the rod members 27 and 28 inresponse to any sensed abnormal projection of the cable 13.

If the sensed projection occurs nearer one rod member than the other,the sensing bar member 39 will be moved into a tilted position insteadof perfectly parallel to its original position, and accordingly, theblocks 33 and 34 will pivot about their respective pivot pins 40 and 41to permit the rod members 27 and 28 to remain in their substantiallyvertical positions illustrated. However, the rod members 27 and 28 mayshift laterally a very slight amount without affecting the operation ofthe device, which shift amount is accommodated by the large clearance ofthe respective bores for the rod members 27 and 28.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects, and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

What is claimed is:

1. Limit switch apparatus mountable adjacent and substantially parallelto the periphery of a cable accepting apparatus for sensing cableprojections beyond the surface comprising: a sensing bar memberincluding a longitudinal axis positioned adjacent the apparatus surfaceand such that projections from the peripheral surface cause movement ofat least one end of said sensing bar in a direction substantially normalto the surface; a separate rod member connected to each end of saidsensing bar member; pivotal mounting means being mounted on the barmember at right angles to the bar member longitudinal axis and coupledto one end of each rod member and thereby permitting pivotal movement ofthe rod member in a plane passing through the sensing bar memberlongitudinal axis facilitating such connection such that movement of oneend of said sensing bar member and said rod member connected theretoresults in substantially no misalignment of said rod members; and motionresponsive means mechanically coupled to the other ends of said rodmembers for actuation thereby in response to said radial motion.

2. Limit switch apparatus, mountable adjacent the peripheral of acylindrical apparatus which is rotatable about its longitudinal axis,for sensing a radial projection from such cylindrical apparatus anywherealong 'such peripheral length, such cylindrical apparatus being rotatably driven by motor means, comprising: a sensing bar member positionedadjacent the peripheral surface of such cylindrical apparatus andparallel to the longitudinal axis thereof whereby the occurrence of aradial projection from such peripheral surface anywhere along the lengththereof causes movement of at least one end of said sensing bar memberin a direction radially outward from such cylindrical apparatus; a pairof rod members each having one end connected to respective opposite endsof said sensing bar member and oriented radially with respect to saidlongitudinal axis of such cylindrical apparatus whereby such radialmovement of said at least one end of said sensing bar member causes acorresponding said rod member to move in a radial direction; and switchmeans mechanically coupled to the other ends of said rod members foractuation thereby in response to said radial motion, said switch meansbeing in control relationship to said motor means for causing stoppingthereof.

3. Limit switch apparatus, mountable adjacent the effective peripheralsurface of a cable as it is wound upon a cylindrical drum which isrotatable about its longitudinal axis, for sensing a radial projectionof such cable from its normal such peripheral surface anywhere along thelength of the drum, such drum being rotatably driven by motor means,comprising: a sensing bar member positioned adjacent such pripheralsurface and parallel thereto whereby the occurrence of a radialprojection of such cable from such peripheral surface anywhere along thelength thereof causes movement of at least one end of said sensing barmember in a direction radially outward from such cylindrical drum; apivot member rotatably connected to respective opposite ends of saidsensing bar member, a pair of rod members each having one end connectedto one of said pivot members for movement independent of the other ofsaid rod members and oriented radially with respect to said longitudinalaxis of such cylindrical drum whereby such radial movement of said atleast one end of said sensing bar member causes a corresponding said rodmember to move in a radial direction with a minimum of stress beingintroduced into the said rod members; and separate switch meansmechanically coupled to the other ends of each of said rod members foractuation thereby in response to said radial motion, said switch meansbeing in control relationship to said motor means for causing stoppingthereof.

References Cited by the Examiner UNITED STATES PATENTS SAMUEL F.COLEMAN, Primary Examiner.

5 HARRISON R. MOSELEY, Examiner.

1. LIMIT SWITCH APPARATUS MOUNTABLE ADJACENT AND SUBSTANTIALLY PARALLELTO THE PERIPHERY OF A CABLE ACCEPTING APPARATUS FOR SENSING CABLEPROJECTIONS BEYOND THE SURFACE COMPRISING: A SENSING BAR MEMBERINCLUDING A LONGITUDINAL AXIS POSITIONED ADJACENT THE APPARATUS SURFACEAND SUCH THAT PROJECTIONS FROM THE PERIPHERAL SURFACE CAUSE MOVEMENT OFAT LEAST ONE SAID SENSING BAR IN A DIRECTION SUBTANTIALLY NORMAL TO THESURFACE; A SEPARATE ROD MEMBER CONNECTED TO EACH END OF SAID SENSING BARMEMBER; PIVOTAL MOUNTING MEANS BEING MOUNTED ON THE BAR MEMBER T RIGHTANGLES TO THE BAR MEMBER LONGITUDINAL AXIS AND COUPLED TO ONE END OFEACH ROD MEMBER AND THEREBY PERMITTING PIVOTAL MOVEMENT OF THE MEMBER INA PLANE PASSING THROUGH THE SENSING BAR MEMBER LONGITUDINAL AXISFACILITATING SUCH CONNECTION SUCH THTAT MOVEMENT OF ONE END OF SAIDSENSING BAR MEMBER AND SAID ROD MEMBER CONNECTED THERETO RESULTS INSUBSTANTIALLY NO MISALIGNMENT OF SAID ROD MEMBERS; AND MOTION RESPONSIVEMEANS MECHANICALLY COUPLED TO THE OTHER ENDS OF SAID ROD MEMBERS FORACTUATION THEREBY IN RESPONSE TO SAID RADIAL MOTION.